Chapter 14 The Digestive System

Transcription

Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 14
The Digestive System and
Body Metabolism
Slides 14.1 – 14.14
Lecture Slides in PowerPoint by Jerry L. Cook
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Digestive System and Body
Metabolism
 Digestion
 Breakdown of ingested food
 Absorption of nutrients into the blood
 Metabolism
 Production of cellular energy (ATP)
 Constructive and degradative cellular
activities
Slide 14.1
Organs of the Digestive System
 Two main groups
 Alimentary canal – continuous coiled hollow
tube
 Accessory digestive organs
Slide 14.2a
Organs of the Digestive System
Figure 14.1
Slide 14.2b
Organs of the Alimentary Canal
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Anus
Slide 14.3
Mouth (Oral Cavity) Anatomy
 Lips (labia) – protect
the anterior opening
 Cheeks – form the
lateral walls
 Hard palate – forms
the anterior roof
 Soft palate – forms
the posterior roof
 Uvula – fleshy
projection of the
soft palate
Figure 14.2a
Slide 14.4
 Vestibule – space
between lips
externally and teeth
and gums internally
 Oral cavity – area
contained by the
teeth
 Tongue – attached at
hyoid and styloid
processes of the
skull, and by the
lingual frenulum
Figure 14.2a
Slide 14.5
 Tonsils
 Palatine tonsils
 Lingual tonsil
Figure 14.2a
Slide 14.6
Processes of the Mouth
 Mastication (chewing) of food
 Mixing masticated food with saliva
 Initiation of swallowing by the tongue
 Allowing for the sense of taste
Slide 14.7
Pharynx Anatomy
 Nasopharynx –
not part of the
digestive system
 Oropharynx –
posterior to oral
cavity
 Laryngopharynx –
below the oropharynx
and connected to
the esophagus
Figure 14.2a
Slide 14.8
Pharynx Function
 Serves as a passageway for air and
food
 Food is propelled to the esophagus by
two muscle layers
 Longitudinal inner layer
 Circular outer layer
 Food movement is by alternating
contractions of the muscle layers
(peristalsis)
Slide 14.9
Esophagus
 Runs from pharynx to stomach through
the diaphragm
 Conducts food by peristalsis
(slow rhythmic squeezing)
 Passageway for food only (respiratory
system branches off after the pharynx)
Slide 14.10
Layers of Alimentary Canal Organs
 Mucosa
 Innermost layer
 Moist membrane
 Surface epithelium
 Small amount of connective tissue
(lamina propria)
 Small smooth muscle layer
Slide 14.11a
 Submucosa
 Just beneath the mucosa
 Soft connective tissue with blood vessels,
nerve endings, and lymphatics
Slide 14.11b
 Muscularis externa – smooth muscle
 Inner circular layer
 Outer longitudinal layer
 Serosa
 Outermost layer – visceral peritoneum
 Layer of serous fluid-producing cells
Slide 14.12
Figure 14.3
Slide 14.13
Alimentary Canal Nerve Plexuses
 All are part of the autonomic nervous
system
 Three separate networks of nerve fibers
 Submucosal nerve plexus
 Myenteric nerve plexus
 Subserous plexus
Slide 14.14
Stomach Anatomy
 Located on the left side of the
abdominal cavity
 Food enters at the cardioesophageal
sphincter
Slide 14.15a
Stomach Anatomy
 Regions of the stomach
 Cardiac region – near the heart
 Fundus
 Body
 Phylorus – funnel-shaped terminal end
 Food empties into the small intestine at
the pyloric sphincter
Slide 14.15b
Stomach Anatomy
 Rugae – internal folds of the mucosa
 External regions
 Lesser curvature
 Greater curvature
Slide 14.16a
Stomach Anatomy
 Layers of peritoneum attached to the
stomach
 Lesser omentum – attaches the liver to the
lesser curvature
 Greater omentum – attaches the greater
curvature to the posterior body wall
 Contains fat to insulate, cushion, and
protect abdominal organs
Slide 14.16b
Stomach Anatomy
Figure 14.4a
Slide 14.17
Stomach Functions
 Acts as a storage tank for food
 Site of food breakdown
 Chemical breakdown of protein begins
 Delivers chyme (processed food) to the
small intestine
Slide 14.18
Specialized Mucosa of the Stomach
 Simple columnar epithelium
 Mucous neck cells – produce a sticky
alkaline mucus
 Gastric glands – secrete gastric juice
 Chief cells – produce protein-digesting
enzymes (pepsinogens)
 Parietal cells – produce hydrochloric acid
 Endocrine cells – produce gastrin
Slide 14.19
Structure of the Stomach Mucosa
 Gastric pits formed by folded mucosa
 Glands and specialized cells are in the
gastric gland region
Slide 14.20a
Structure of the Stomach Mucosa
Figure 14.4b, c
Slide 14.20b
Small Intestine
 The body’s major digestive organ
 Site of nutrient absorption into the blood
 Muscular tube extending form the
pyloric sphincter to the ileocecal valve
 Suspended from the posterior
abdominal wall by the mesentery
Slide 14.21
Subdivisions of the Small Intestine
 Duodenum
 Attached to the stomach
 Curves around the head of the pancreas
 Jejunum
 Attaches anteriorly to the duodenum
 Ileum
 Extends from jejunum to large intestine
Slide 14.22
Chemical Digestion in the Small
Intestine
 Source of enzymes that are mixed with
chyme
Intestinal cells
Pancreas
 Bile enters from the gall bladder
Slide 14.23a
Chemical Digestion in the Small
Intestine
Figure 14.6
Slide 14.23b
Villi of the Small Intestine
 Fingerlike
structures formed
by the mucosa
 Give the small
intestine more
surface area
Figure 14.7a
Slide 14.24
Microvilli of the Small Intestine
 Small projections of the
plasma membrane
 Found on absorptive cells
Figure 14.7c
Slide 14.25
Structures Involved in Absorption of
Nutrients
 Absorptive cells
 Blood capillaries
 Lacteals (specialized
lymphatic capillaries)
Figure 14.7b
Slide 14.26
Folds of the Small Intestine
 Called circular folds or plicae circulares
 Deep folds of the mucosa and
submucosa
 Do not disappear when filled with food
 The submucosa has Peyer’s patches
(collections of lymphatic tissue)
Slide 14.27
Large Intestine
 Larger in diameter, but shorter than the
small intestine
 Frames the internal abdomen
Slide 14.28
Large Intestine
Figure 14.8
Slide 14.28
Functions of the Large Intestine
 Absorption of water
 Eliminates indigestible food from the
body as feces
 Does not participate in digestion of food
 Goblet cells produce mucus to act as a
lubricant
Slide 14.29
Structures of the Large Intestine
 Cecum – saclike first part of the large
intestine
 Appendix
Accumulation of lymphatic tissue that
sometimes becomes inflamed
(appendicitis)
Hangs from the cecum
Slide 14.30a
Structures of the Large Intestine
 Colon
 Ascending
 Transverse
 Descending
 S-shaped sigmoidal
 Rectum
 Anus – external body opening
Slide 14.30b
Modifications to the Muscularis
Externa in the Large Intestine
 Smooth muscle is reduced to three
bands (teniae coli)
 Muscle bands have some degree of
tone
 Walls are formed into pocketlike sacs
called haustra
Slide 14.31
Accessory Digestive Organs
 Salivary glands
 Teeth
 Pancreas
 Liver
 Gall bladder
Slide 14.32
Salivary Glands
 Saliva-producing glands
 Parotid glands – located anterior to ears
 Submandibular glands
 Sublingual glands
Slide 14.33
Saliva
 Mixture of mucus and serous fluids
 Helps to form a food bolus
 Contains salivary amylase to begin
starch digestion
 Dissolves chemicals so they can be
tasted
Slide 14.34
Teeth
 The role is to masticate (chew) food
 Humans have two sets of teeth
 Deciduous (baby or milk) teeth
 20 teeth are fully formed by age two
Slide 14.35a
Teeth
 Permanent teeth
 Replace deciduous teeth beginning
between the ages of 6 to 12
 A full set is 32 teeth, but some people do
not have wisdom teeth
Slide 14.35b
Classification of Teeth
 Incisors
 Canines
 Premolars
 Molars
Slide 14.36a
Classification of Teeth
Figure 14.9
Slide 14.36b
Regions of a Tooth
 Crown – exposed
part
 Outer enamel
 Dentin
 Pulp cavity
 Neck
 Region in contact
with the gum
 Connects crown to
root
Figure 14.10
Slide 14.37a
Regions of a Tooth
 Root
 Periodontal
membrane
attached to the
bone
 Root canal carrying
blood vessels and
nerves
Figure 14.10
Slide 14.37b
Pancreas
 Produces a wide spectrum of digestive
enzymes that break down all categories of food
 Enzymes are secreted into the duodenum
 Alkaline fluid introduced with enzymes
neutralizes acidic chyme
 Endocrine products of pancreas
 Insulin
 Glucagons
Slide 14.38
Liver
 Largest gland in the body
 Located on the right side of the body
under the diaphragm
 Consists of four lobes suspended from
the diaphragm and abdominal wall by
the falciform ligament
 Connected to the gall bladder via the
common hepatic duct
Slide 14.39
Bile
 Produced by cells in the liver
 Composition
 Bile salts
 Bile pigment (mostly bilirubin from the
breakdown of hemoglobin)
 Cholesterol
 Phospholipids
 Electrolytes
Slide 14.40
Gall Bladder
 Sac found in hollow fossa of liver
 Stores bile from the liver by way of the
cystic duct
 Bile is introduced into the duodenum in
the presence of fatty food
 Gallstones can cause blockages
Slide 14.41
Processes of the Digestive System
 Ingestion – getting food into the mouth
 Propulsion – moving foods from one
region of the digestive system to
another
Slide 14.42a
 Peristalsis – alternating
waves of contraction
 Segmentation – moving
materials back and forth
to aid in mixing
Figure 14.12
Slide 14.42b
 Mechanical digestion
 Mixing of food in the mouth by the tongue
 Churning of food in the stomach
 Segmentation in the small intestine
Slide 14.43
 Chemical Digestion
 Enzymes break down food molecules into
their building blocks
 Each major food group uses different
enzymes
 Carbohydrates are broken to simple sugars
 Proteins are broken to amino acids
 Fats are broken to fatty acids and alcohols
Slide 14.44
 Absorption
 End products of digestion are absorbed in
the blood or lymph
 Food must enter mucosal cells and then
into blood or lymph capillaries
 Defecation
 Elimination of indigestible substances as
feces
Slide 14.45
Figure 14.11
Slide 14.46
Control of Digestive Activity
 Mostly controlled by reflexes via the
parasympathetic division
 Chemical and mechanical receptors are
located in organ walls that trigger
reflexes
Slide 14.47a
Control of Digestive Activity
 Stimuli include:
 Stretch of the organ
 pH of the contents
 Presence of breakdown products
 Reflexes include:
 Activation or inhibition of glandular
secretions
 Smooth muscle activity
Slide 14.47b
Digestive Activities of the Mouth
 Mechanical breakdown
 Food is physically broken down by chewing
 Chemical digestion
 Food is mixed with saliva
 Breaking of starch into maltose by salivary
amylase
Slide 14.48
Activities of the Pharynx and
Esophagus
 These organs have no digestive function
 Serve as passageways to the stomach
Slide 14.49
Deglutition (Swallowing)
 Buccal phase
 Voluntary
 Occurs in the mouth
 Food is formed into a bolus
 The bolus is forced into the pharynx by the
tongue
Slide 14.50
 Pharyngeal-esophageal phase
 Involuntary transport of the bolus
 All passageways except to the stomach are
blocked
 Tongue blocks off the mouth
 Soft palate (uvula) blocks the
nasopharynx
 Epiglottis blocks the larynx
Slide 14.51a
 Pharyngeal-esophogeal phase
(continued)
 Peristalsis moves the bolus toward the
stomach
 The cardioesophageal sphincter is opened
when food presses against it
Slide 14.51b
Figure 14.13
Slide 14.52
Food Breakdown in the Stomach
 Gastric juice is regulated by neural and
hormonal factors
 Presence of food or falling pH causes
the release of gastrin
 Gastrin causes stomach glands to
produce protein-digesting enzymes
 Hydrocholoric acid makes the stomach
contents very acidic
Slide 14.53
Necessity of an Extremely Acid
Environment in the Stomach
 Activates pepsinogen to pepsin for
protein digestion
 Provides a hostile environment for
microorganisms
Slide 14.54
Digestion and Absorption in the
Stomach
 Protein digestion enzymes
 Pepsin – an active protein digesting
enzyme
 Rennin – works on digesting milk protein
 The only absorption that occurs in the
stomach is of alcohol and aspirin
Slide 14.55
Propulsion in the Stomach
 Food must first be well mixed
 Rippling peristalsis occurs in the lower
stomach
Figure 14.14
Slide 14.56a
Propulsion in the Stomach
 The pylorus meters out chyme into the
small intestine (30 ml at a time)
 The stomach empties in four to six
hours
Figure 14.14
Slide 14.56b
Digestion in the Small Intestine
 Enzymes from the brush border
 Break double sugars into simple sugars
 Complete some protein digestion
 Pancreatic enzymes play the major
digestive function
 Help complete digestion of starch
(pancreatic amylase)
 Carry out about half of all protein digestion
(trypsin, etc.)
Slide 14.57a
Digestion in the Small Intestine
 Pancreatic enzymes play the major
digestive function (continued)
 Responsible for fat digestion (lipase)
 Digest nucleic acids (nucleases)
 Alkaline content neutralizes acidic chyme
Slide 14.57b
Stimulation of the Release of Pancreatic
Juice
 Vagus nerve
 Local hormones
 Secretin
 Cholecystokinin
Figure 14.15
Slide 14.58
Absorption in the Small Intestine
 Water is absorbed along the length of
the small intestine
 End products of digestion
 Most substances are absorbed by active
transport through cell membranes
 Lipids are absorbed by diffusion
 Substances are transported to the liver
by the hepatic portal vein or lymph
Slide 14.59
Propulsion in the Small Intestine
 Peristalsis is the major means of
moving food
 Segmental movements
 Mix chyme with digestive juices
 Aid in propelling food
Slide 14.60
Food Breakdown and Absorption in
the Large Intestine
 No digestive enzymes are produced
 Resident bacteria digest remaining
nutrients
 Produce some vitamin K and B
 Release gases
 Water and vitamins K and B are absorbed
 Remaining materials are eliminated via
feces
Slide 14.61
Propulsion in the Large Intestine
 Sluggish peristalsis
 Mass movements
 Slow, powerful movements
 Occur three to four times per day
 Presence of feces in the rectum causes
a defecation reflex
 Internal anal sphincter is relaxed
 Defecation occurs with relaxation of the
voluntary (external) anal sphincter
Slide 14.62
Nutrition
 Nutrient – substance used by the body
for growth, maintenance, and repair
 Categories of nutrients
 Carbohydrates
 Lipids
 Proteins
 Vitamins
 Mineral
 Water
Slide 14.63
Dietary Sources of Major Nutrients
 Carbohydrates
 Most are derived from plants
 Exceptions: lactose from milk and small
amounts of glycogens from meats
 Lipids
 Saturated fats from animal products
 Unsaturated fats from nuts, seeds, and
vegetable oils
 Cholesterol from egg yolk, meats, and milk
products
Slide 14.64
 Proteins
 Complete proteins – contain all essential
amino acids
 Most are from animal products
 Legumes and beans also have proteins,
but are incomplete
 Vitamins
 Most vitamins are used as cofactors and
act with enzymes
 Found in all major food groups
Slide 14.65
 Minerals
 Play many roles in the body
 Most mineral-rich foods are vegetables,
legumes, milk, and some meats
Slide 14.66
Metabolism
 Chemical reactions necessary to
maintain life
 Catabolism – substances are broken down
to simpler substances
 Anabolism – larger molecules are built from
smaller ones
 Energy is released during catabolism
Slide 14.67
Carbohydrate Metabolism
 The body’s preferred source to produce
cellular energy (ATP)
 Glucose (blood sugar) is the major
breakdown product and fuel to make
ATP
Figure 14.16
Slide 14.68
Cellular Respiration
 Oxygen-using events take place within the
cell to create ATP from ADP
 Carbon leaves cells as carbon dioxide (CO2)
 Hydrogen atoms are combined with oxygen
to form water
 Energy produced by these reactions adds a
phosphorus to ADP to produce ATP
 ATP can be broken down to release energy
for cellular use
Slide 14.69
Metabolic Pathways Involved in
 Glycolysis – energizes a glucose
molecule so that it can be split into two
pyruvic acid molecules and yield ATP
Slide 14.70a
Figure 14.17
Slide 14.70b
 Krebs cycle
 Produces virtually all the carbon dioxide
and water resulting from cell respiration
 Yields a small amount of ATP
Slide 14.71
 Electron transport chain
 Hydrogen atoms
removed during
glycolysis and
the Krebs cycle
are delivered to
protein carriers
Figure 14.18
Slide 14.72a
 Electron transport chain (continued)
 Hydrogen is
split into
hydrogen ions
and electrons
in the
mitochondria
Figure 14.18
Slide 14.72b
 Electron transport chain (continued)
 Electrons give
off energy in a
series of steps
to enable the
production of
ATP
Figure 14.18
Slide 14.72c
Fat Metabolism
 Handled mostly by the liver
 Use some fats to make ATP
 Synthesize lipoproteins, thromboplastin,
and cholesterol
 Release breakdown products to the blood
 Body cells remove fat and cholesterol to
build membranes and steroid hormones
Slide 14.73
Use of Fats for ATP Synthesis
 Fats must first be broken down to acetic
acid
 Within mitochondira, acetic acid is
completely oxidized to produce water,
carbon dioxide, and ATP
Slide 14.74
Protein Metabolism
 Proteins are conserved by body cells
because they are used for most cellular
structures
 Ingested proteins are broken down to
amino acids
Slide 14.75a
Protein Metabolism
 Cells remove amino acids to build
proteins
 Synthesized proteins are actively
transported across cell membranes
 Amino acids are used to make ATP only
when proteins are overabundant or
there is a shortage of other sources
Slide 14.75b
Production of ATP from Protein
 Amine groups are removed from
proteins as ammonia
 The rest of the protein molecule enters
the Krebs cycle in mitochondria
 The liver converts harmful ammonia to
urea which can be eliminated in urine
Slide 14.76
Role of the Liver in Metabolism
 Several roles in digestion
 Detoxifies drugs and alcohol
 Degrades hormones
 Produce cholesterol, blood proteins
(albumin and clotting proteins)
 Plays a central role in metabolism
Slide 14.77
Metabolic Functions of the Liver
 Glycogenesis
 Glucose molecules are converted to
glycogen
 Glycogen molecules are stored in the liver
 Glycogenolysis
 Glucose is released from the liver after
conversion from glycogen
 Gluconeogenesis
 Glucose is produced from fats and proteins
Slide 14.78
Figure 14.20
Slide 14.79
 Fats and fatty acids are picked up by
the liver
 Some are oxidized to provide energy for
liver cells
 The rest are broken down into simpler
compounds and released into the blood
Slide 14.80
Cholesterol Metabolism
 Functions of cholesterol
 Serves as a structural basis of steroid
hormones and vitamin D
 Is a major building block of plasma
membranes
 Most cholesterol is produced in the liver
and is not from diet
Slide 14.81
Cholesterol Transport
 Cholesterol and fatty acids cannot freely
circulate in the bloodstream
 They are transported by lipoproteins
(lipid-protein complexes)
 Low-density lipoproteins (LDLs) transport to
body cells
 High-density lilpoproteins (HDLs) transport
from body cells to the liver
Slide 14.82
Body Energy Balance
 Energy intake = total energy output
(heat + work + energy storage)
 Energy intake is liberated during food
oxidation
 Energy output
 Heat is usually about 60%
 Storage energy is in the form of fat or
glycogen
Slide 14.83
Regulation of Food Intake
 Body weight is usually relatively stable
 Energy intake and output remain about
equal
 Mechanisms that may regulate food
intake
 Levels of nutrients in the blood
 Hormones
 Body temperature
 Psychological factors
Slide 14.84
Metabolic Rate and Body Heat
Production
 Basic metabolic rate (BMR) – amount of
heat produced by the body per unit of
time at rest
 Factors that influence BMR
 Surface area – small body usually has
higher BMR
 Gender – males tend to have higher BMR
Slide 14.85a
Metabolic Rate and Body Heat
Production
 Factors that influence BMR (continued)
 Age – children and adolescents have a
higher BMR
 The amount of thyroxine produced is the
most important control factor
 More thyroxine means higher metabolic
rate
Slide 14.85b
Total Metabolic Rate (TMR)
 Total amount of kilocalories the body
must consume to fuel ongoing activities
 TMR increases with an increase in body
activity
 TMR must equal calories consumed to
maintain homeostasis and maintain a
constant weight
Slide 14.86
Body Temperature Regulation
 Most energy is released as foods are
oxidized
 Most energy escapes as heat
Slide 14.87a
Body Temperature Regulation
 The body has a narrow range of
homeostatic temperature
 Must remain between 35.6° to 37.8°C
(96° to 100° F)
 The body’s thermostat is in the
hypothalamus
 Initiates heat-loss or heat-promoting
mechanisms
Slide 14.87b
Heat Promoting Mechanisms
 Vasoconstriction of blood vessels
 Blood is rerouted to deeper, more vital body
organs
 Shivering – contraction of muscles
produces heat
Slide 14.88
Heat Loss Mechanisms
 Heat loss from the skin via radiation and
evaporation
 Skin blood vessels and capillaries are
flushed with warm blood
 Evaporation of perspiration cools the skin
Slide 14.89
Body
Temperature
Regulation
Figure 14.21
Slide 14.90
Developmental Aspects of the
Digestive System
 The alimentary canal is a continuous tube
by the fifth week of development
 Digestive glands bud from the mucosa of
the alimentary tube
 The developing fetus receives all
nutrients through the placenta
 In newborns, feeding must be frequent,
peristalsis is inefficient, and vomiting is
common
Slide 14.91
Digestive System
 Teething begins around age six months
 Metabolism decreases with old age
 Middle age digestive problems
 Ulcers
 Gall bladder problems
Slide 14.92a
Digestive System
 Activity of digestive tract in old age
 Fewer digestive juices
 Peristalsis slows
 Diverticulosis and cancer are more
common
Slide 14.92b

Chapter 14 The Digestive System

Transcription

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